Field of the Invention
The present invention relates to an electronic module for onboard aviation equipment, and to equipment for an aviation vehicle such as an aircraft.
Brief Discussion of the Related Art
It is known that aircraft and aircraft equipment are subjected in operation to mechanical and thermal stresses that together severely test the structures of said aircraft and of their equipment. Those stresses apply in full or in part both during flight proper and during stages of takeoff, landing, braking or taxiing on the ground, and in a variety of environments depending on the geographical regions in which the aircraft are used. This leads to stresses of large amplitude making it difficult to design aircraft and aircraft equipment.
By way of example, in the vicinity of an aircraft wheel the thermal amplitudes under consideration extend from −60° C. (for several hours in flight) to a value that under some circumstances may be as high as +180° C., or even 4-200° C. on landing (with the high temperature lasting for at least about one hour) because of the temperature rise in the wheel brakes, and this applies for thousands of cycles. In addition to temperature, there are also impacts and vibration on landing that can lead to mechanical damage to equipment.
Electronics modules and circuits are particularly sensitive to such stresses. In particular:                temperature variations give rise to expansion and contraction cycles for circuit components;        high temperature exposure that is prolonged (in terms of accumulated duration) causes intermetallic compounds to be generated between the materials present, thereby weakening assemblies and possibly leading to sudden breaks in the event of impacts or during thermal cycling; and        at low temperatures rigid materials may be found to be weak in the event of impacts (ductile/brittle transitions).        
In addition, when such components are made of different materials, as is usually the case, differential expansions and contractions appear that lead to stresses in heterogeneous assemblies and components.
Certain circuits are embedded in plastics material such as an epoxy resin in order to protect them from moisture. Given the thickness of epoxy needed for such a protection function, the differential expansions may be such as to break connections between the epoxy and the circuit, thereby letting moisture in or leading to high levels of stress on the connections between surface components and the circuit.
There also exist modules comprising circuits enclosed in hermetic packages containing inert gas or a vacuum. That serves to reduce problems of differential expansions and of general aging, but considerably increases the weight, the size, the complexity, and thus the cost of such modules, while also making the necessary inspection operations more complicated.